A variety of new techniques are being used to monitor the afferent and efferent neural activity in the spinal cord of intact cats during normal and perturbed locomotion. Flexible wire electrodes in the lumbar dorsal root ganglia (DRG) and ventral roots record stable, identifiable unit activity which is correlated with kinesiological data from chronically implanted gauges of muscle force, length, and EMG activity developed for this project. Neurons are characterized by conduction velocity, anatomical origin, and modality using spike-triggered averaging of EMG signals and neurograms obtained from specially designed nerve cuff electrodes implanted around peripheral nerves. The reflex effects of various electrical stimuli to motor and cutaneous nerves are systematically examined as they vary through the step cycle. The normal functional use of the various hindlimb muscles is being surveyed during a variety of normal behaviors in an attempt to correlate these patterns with their anatomical specializations regarding muscle fiber type and orientation and proprioceptive feedback. A new study has been initiated in which the activity in the cuneate nucleus, the first ascending relay for sensory information from the cat forelimb, will be chronically recorded to study plasticity following peripheral nerve ligation.